My first nightmare, around three or four years old, was also with aliens.
Mom had an alien-shaped "green man" trinket. In my dream, aliens, which looked like the trinket, had arrived and everyone they touched turned into them. The only people left were my best friend and me. We were surrounded by a tight circle of aliens. A bright thing -which I knew had aliens- was located on top of my friend and me and started descending upon us. I was so scared, then I woke up.